The present invention relates to a method for fabricating a lens unit, specifically to a method for fixing an inter-barrel member in an optical path. The present invention relates to a lens unit fabricated by the method and an imaging apparatus including the lens unit.
In a lens unit employed in an imaging apparatus such as camera, an inter-barrel member such as a shutter unit and an anti-shake unit for driving an optical member to stabilize image is disposed in an intermediate portion of the lens barrel (see patent documents 1, 2).
Patent Document 1:
Japanese Laid-open patent publication No. 2002-341223
Patent Document 2:
U.S. Pat. No. 6,661,970 B2
FIG. 6 shows a construction of a conventional typical lens unit 51. The lens unit 51 has a single lens barrel comprising a front lens barrel 52 on a subject side in an optical-axis direction and a rear lens barrel 53 on an imaging surface side in the optical-axis direction. The lens unit 51 comprises, in the order from the object side, a first lens 54 fixed on the tip end of the front lens barrel 52, a second lens 55 movable in the optical-axis direction inside the front lens barrel 52, a shutter unit (inter-barrel member) 56 inserted between the front lens barrel 52 and the rear lens barrel 53 and a third lens 57 fixed on the rear lens barrel 53. The front lens barrel 52 and the rear lens barrel 53 have flange portions 52a and 53a, respectively formed by extending the facing end portions toward outside. The flange portion 52a and the shutter unit 56 are fixed to the flange portion 53a by means of screws 58.
In the lens unit 51, the distance between the first lens 54 or the second lens and the third lens 57 is determined by the sizes of the front lens barrel and the rear lens barrel 53 and the thickness of the shutter unit 56. The relative positions of each lens 54, 55, 57 involved in imaging need to be exactly determined and the dimensions of the front lens barrel 52, the rear lens barrel 53 and the shutter unit 56 need to be precisely fabricated. Enhancing the accuracy of the dimension of the shutter unit constituted by combining a plurality of members causes a problem of high fabrication cost.
FIG. 7 shows a construction of a conventional lens unit 51′ in which the accuracy of the dimension of the shutter unit 56 is not required. In the lens unit 51′, the flange portion 52a of the front lens barrel 52 and the flange portion 53a of the rear lens barrel 53 are directly fixed by means of screws 58, while the shutter unit 56 is fixed by means of screws 59 on a seat portion 53b protruding inside the rear lens barrel 53. The relative positions of the lenses 54, 55, 57 are determined by the front lens barrel 52 and the rear lens barrel 53 irrespective of the dimension of the shutter unit 56. However, in this construction, as the seat portion 53b protruding inside the rear lens barrel 53 is provided and the screws 59 are arranged inside the lens barrels 52, 53, the diameters of the lens barrels 52, 53 need to be enlarged so that the seat portion 53b and the screws 59 will not interfere with the optical path. Thus, there has been a disadvantage that it is not possible to meet the needs of miniaturization to the lens unit.